1. Field of the Invention
The invention relates to a charged particle beam device for inspecting or structuring a specimen by means of a charged particle beam. In particular, the invention relates to a charged particle beam device having means to direct gas towards the specimen.
2. Description of the Related Art
Technologies such as microelectronics, micromechanics and biotechnology have created a high demand for structuring and probing specimens within the nanometer scale. On such a small scale, probing or structuring is often performed with charged particle beams which are generated and focused in charged particle beam devices. Examples of charged particle beam devices are electron microscopes as well as electron or ion beam pattern generators. Charged particle beams, in particular ion and electron beams, offer superior spatial resolution compared to photon beams, due to their short wave lengths at a comparable particle energy.
While charged particle beam devices are able to meet high spatial resolution requirements, they often carry the disadvantage that they charge the specimen in the region where the primary charged particle beam impinges onto the specimen during a scan. Charging of the specimen is particularly severe if the surface of the specimen comprises electrically insulating or poorly conducting material, such as biological tissue, or oxide regions of a semiconductor integrated circuit. In these cases, diversion of the excess charge generated by the impinging charged particle beam on the specimen is so slow that the charging generates potentials on the specimen surface that are high enough to deform or deflect the impinging charged particle beam. As a consequence, a scan of the charged particle beam over the specimen is distorted which in turn deteriorates the spatial resolution of the charged particle beam device.
Charging is even more difficult for charged particle beam devices that inspect a specimen through the detection of secondary charged particles generated by the charged particle beam on the specimen. The potentials near the surface of the specimen generated through charging can prevent secondary charged particles from escaping from the surface, or deflect them in a way that they do not reach the sensitive area of the detector. Both lead to a loss of spatial resolution for the inspection.
There have been several techniques developed to reduce charging. One of them is to adjust the energy of the primary charged particles to a value where the emission rate of secondary charged particles balances the flux of the incoming charged particle beam, as described e.g. U.S. Pat. No. 6,066,849. In this case, excess charge in the regions of beam incidence can be kept close to zero. However, this technique does not allow the energy of the charged particle beam to be freely chosen which in turn excludes many useful applications in the field of charged particle beam microscopy and structuring.
Another technique to reduce charging of a specimen has been proposed in patent application EP 0 969 494 A1. The technique uses a gas supply system to introduce a gas by means of a gas nozzle into the electron beam near the specimen. The gas picks up some or all of the excess charge from the specimen when it comes in contact with the surface of the specimen. The higher the concentration of the ionized gas near the specimen, the higher the decharging rate.
It should be mentioned that the use of a gas supply system near the specimen is not limited to a decharging of the specimen. Instead, the gas may also be used to interact with the specimen in some other way. For example, the gas may be used to etch the specimen or to provide a material layer (vapor deposition) in the region where the charged particle beam impinges onto the specimen.
Decharging, etching or depositing with present gas supply systems, however, requires a significant amount of gas to be injected into the vacuum. This can load the vacuum pump to such a degree that it damages the pump. In addition, the introduced gas worsens the overall vacuum and widens the focus of the charged particle beam due to collisions between the charged particle beam and the gas. Further, the large amount of gas near the high electric fields of the beam optical lens can lead to arcing which destroys the beam optics.